Program in Laboratory Research in Pediatric Oncology-Hematology: To continue to make progress in Pediatric Oncology-Hematology (POH), we need to perpetuate the pool of talented and trained POH physician-scientists and PhD scientists who will make POH-relevant discoveries and provide investigative leadership. Nevertheless, in the field of POH, there continues to be a shortage of young investigators with extensive laboratory research expertise. In the current funding period (2002-2008), this grant has already supported superb laboratory research training for an outstanding group of 21 physician-scientists and 8 PhD scientists who have demonstrated a high degree of productivity and commitment to careers in cancer research. In addition, these trainees have strengthened the laboratory research base in POH in the Johns Hopkins Medical Institutions (JHMI). This application again seeks support for 10 interdisciplinary postdoctoral research fellowship positions per year to fund the research training that is the major ingredient of the recently combined Johns Hopkins University/National Cancer Institute (NCI) Subspecialty Fellowship Training Program in POH (Joint Fellowship Training Program). Two groups of postdoctoral fellows will be supported by the grant proposed herein. The major group of trainees will be composed of physician-scientists, since the laboratory research training of academic POH physician-scientists is the primary objective of this training program. These highly selected physician- scientists will have completed the clinical year of their fellowships in the Joint Fellowship Training Program. The second (smaller) group of trainees will be composed of PhD postdoctoral scientists working at JHMI on projects highly relevant to the biology of childhood cancer and blood diseases. These strongly qualified postdoctoral trainees will be provided intensive 3-year research experiences that will prepare them for careers in cancer research. Trainees will work on projects relevant to the biology of childhood cancer and blood diseases, in the laboratories of leading scientists in the field. The trainees and their mentors will participate in an interactive, dynamic research environment bridging the JHMI and the National Institutes of Health (NIH), with an emphasis on translational research. Summary of relevance to public health: This program provides postdoctoral education, training, and experience in field-leading research on childhood cancer and blood diseases, principally for physician- scientist trainees during their subspecialty fellowships in pediatric oncology-hematology.